PM7340 S/UNI-IMA-8
PRELIMINARY
INVERSE MULTIPLEXING OVER ATM
DATA SHEET
PMC-2001723
ISSUE 3
INVERSE MULTIPLEXING OVER ATM
Links may also be unchannelized. In that case, all data bytes on that link belong
to the virtual link. The TCAS performs a table look-up to identify the link to which
a data byte belongs using only the outgoing link identity, as no time-slots are
associated with unchannelized links. The link clock is only active during bit-times
containing data to be transmitted; it is inactive during bit-times that are to be
ignored by the downstream devices, such as framing and overhead bits.
10.5.2 Rx Clock/Data (RCAS)
The S/UNI-IMA-8 provides up to eight 2-pin Clock/Data serial interfaces for
interconnecting to T1/E1 framers. Each link is independent and has its own
associated clock. For each link, the data is sent through a serial to parallel
conversion to form data bytes. The data bytes are multiplexed, in byte serial
format, for delivery to the TC layer. In the event where multiple streams have
accumulated a byte of data, multiplexing is performed on a fixed priority basis,
with link #0 having the highest priority and link #7 the lowest.
For the clock and data interface, the framer must gap the clock for all framing bits
for T1 and for the framinging byte for E0.
Links containing a T1 or an E1 stream may be channelized. For channelized
links, the link clock is only active during time-slots 1 to 24 of a T1 stream; it is
inactive during the frame bit. Similarly, the clock is only active during time-slots 1
to 31 of an E1 stream and inactive during the FAS and NFAS framing bytes.
Each time-slot may be independently configured to be provisioned (contain valid
data) or unprovisioned. The RCAS performs a table lookup to assign the
provisioned time-slots to a virtual link. After the selected timeslots are grouped
into a virtual link, virtual links are referred to as links. This look-up should be used
to remove byte 16 of the E1 frame, since byte 16 contains signaling data not ATM
data and is also used to implement a fractional T1 or E1. The first bit of time-slot
1 of a channelized link is identified by noting the absence of the clock and its re-
activation.
Links may also be unchannelized. In this mode, all data is assumed to be valid
ATM data. The link clock is only active during bit times containing data to be
processed and inactive during bits that are to be ignored by the RCAS, such as
framing and overhead bits.
The RCAS provides diagnostic line-side loopback that is selectable on a per-
channel basis. When a channel is in diagnostic loopback, data on the received
links originally destined for that channel is ignored. Transmit data of that channel
is substituted in its place.
PROPRIETARY AND CONFIDENTIAL TO PMC-SIERRA, INC., AND FOR ITS CUSTOMERS’ INTERNAL USE
88
PMC [ PMC-SIERRA, INC ]
